Dirty Human Killer (An Undertale Fic)
by TheGodOfHyperdeath
Summary: Mettaton seems ready to devour the human child's soul, but there's only one thing standing in his way: a bad time.


**Dirty Human Killer (Sans vs Mettaton)**

(Author's Note: I own basically none of this. All credit goes to Toby Fox. This event is non-canon and is also my first fanfic. It is supposed to occur on a Pacifist Run of Undertale. Please leave your criticism in the comments! Thanks!)

Mettaton sat in Alphys' lab, alone and in the harrowing dark, scanning the glowing, LED screen that was constantly following the human child as it trekked across the underground in search of Asgore's kingdom. He knew that it was only a matter of time before the child found its way to Mettaton and he could absorb the human's soul and rise up to entertain the masses of humans. Then, if his luck worked in favour of him, he could devour more and more human souls, becoming a God amongst mortal men – a God of fabulousness, he chuckled to himself in a robotic tone.

"Oh, hey Mettaton." A deep and drowsy tone muttered from behind him. Mettaton swivelled around, allowing his scanners to detect one short, stout skeleton wearing a blue hoodie.

"Who… who are you? How did you get in?" Mettaton asked, with his right arm rubbing the top of his cuboid-shaped body in confusion.

"My name is Sans and, er, I took a shortcut."

"Wait, you're Sans? _The_ Sans? Alphys told me all about you but, err… you're not what I expected…" Mettaton questioned, slightly dumbfounded.

"Yeah, well, anyway, I, er, wanted to ask you a favour." Sans replied, ignoring him.

"Fire away." Mettaton insisted, with both thumbs up.

"Yeah, er, well, it's about the human. You see, Alphys told me that you wanted the human soul so you could get back to the surface, right? Y'see, I can't let that happen."

"Why ever not?"

"Well, I made a promise to an old friend that I'd protect the li'l kiddo and, as you probably know," Sans said, indicating towards the screen, "the child hasn't been any trouble. It spared my brother and everyone else it came into contact with, so I've gotta follow through on what I promised my friend. So, could you please not murder… it?"

"Yeah… I'm afraid I'm gonna have to say no. Sorry, friend." Mettaton smugly replied. Sans still smiled, eyes closed.

"Hmm... let me rephrase that for you…" Sans declared, tonelessly.

His eyes reopened, his smile still eerily resilient, but his pupils were inexplicably gone.

"Hurt the human child and you're gonna have a bad time."

After what seemed like hours of wrecking Mettaton, Sans flicked his wrist, hurling his victim against the clear, white wall of Alphys' lab. Dented and smashed, the mostly-dead robot knew he had no hope of beating his foe.

"Take it from me, bro, some day you just gotta learn when to quit… and that day is today."

"Jeez, Undyne once told me you were strong but… I had no idea…" his dying voice rasped, his white hands grasping his cracked lights.

"Don't say I didn't warn you." Sans snorted, kicking the pile of scraps and broken shards of glass that humbly lay before him.

"B… b… b… bu-… but I-I-I'm not r-r-ready to give up y-yet, S-Sans." Mettaton wheezed, motors whirling at a rapid rate just to push out those words from his blown-out speakers. Suddenly, the torn metal started shifting and shuffling. Within mere moments, a humanoid figure made of the scraps appeared. With a polished black design and a pink glow emanating from his chest, Mettaton was now an elegant android. Sans watched, his soulless, empty gaze fixing on Mettaton's sleek body. Mettaton giggled.

"Soak it in, sweetie. You've got an exclusive look at my newest form! Ooh, darling, think about what others would give to be in your shoes right now!"

"I'll kill you." Sans snarled.

Mettaton outstretched his arm, commanding dozens upon dozens of miniature versions of his original form to attack. Roughly sixty, maybe seventy, mini-Mettatons soared through the air at Sans, who evaded every single one and they all crashed into the wall, causing several minuet explosions. Mettaton gasped at how easily his bots were defeated, and pounced straight for Sans.

Sans quickly sidestepped as Mettaton flung himself towards the ground next to him. Sans then gripped Mettaton's wrist and launched him against the wall at the other end of the lab with little effort. Mettaton groaned as his entire body slammed into the wall. Staggering to his feet, Mettaton smiled. From talking to Alphys and Undyne, he knew Sans had one fatal weakness – his laziness. Sans would tire out really easily so, as long as Mettaton could keep going, Sans wasn't going to last long. Mettaton splayed his fingers again, signalling to thousands of mini-bots an attack command.  
"Execute him!" He roared, summoning hordes of charging mini-bots at his will. They swarmed the room, going straight for Sans. Sans grinned, summoning two white dragon heads from nothing. They opened their wide mouths and released a mighty blast of sheer energy. The two destructive beams disintegrated every single mini-Mettaton in sight, alongside most of Alphys' lab. Mettaton gasped, more hurt by shock than the recoil of the attack. Mettaton's scanners displayed a single message: "Keep attacking, he can't keep dodging forever."

Mettaton swiped and kicked repeatedly at Sans in a rhythmic pattern. He kicked in a circular fashion but Sans ducked, dodged, dipped and dived from every single blow. Again and again, kick after kick, Sans wasn't even slightly bothered. His calm, collected evasion of every offensive manoeuvre thrown at him frustrated Mettaton. Mettaton was giving everything he had, but Sans didn't even blink. There was no panting, no screams, nothing to validate Mettaton's attacks. And, of course, Mettaton's systems relayed the same message again and again: "Keep attacking, he can't keep dodging forever." as if that was gonna help.

"Face it, Mettaton, you ain't gonna win." He muttered to himself, panting.

"Given up yet?" Sans jeered, wiping a couple sweat drops from his head with his blue sleeve.  
"Uh, ye-…" Mettaton started, before freezing in the middle of the sentence. "Wait! That's it! That's it, isn't it?!" He thought to himself, "Sans just wiped his head for sweat. He _is_ tired of fighting! He's slowing down! I can't give up the human soul just yet! I've got to keep fighting!"

"Uh, look. I just wanted to tell you, before you do anything _unbelievably stupid_ , to back down now. I know you're considering having another crack at me, and, credit where it's due, your determination is admirable – but I'm telling you right now that you're really not gonna like what's gonna happen next." Mettaton stood, eyes staring straight into Sans'. His scanners displayed another message: "Show him your true power".

Mettaton nodded. One of his hands inverted and shuffled around, turning into a minigun-like weapon. His back opened up, revealing two wings formed of solid light. His shoulders broadened, his boots became more pointed and long spikes emerged his heels, ankles and shoulders. Just under half of his face slipped off, revealing a black endoskeleton and one purple glowing eye.

"I see you've made your decision, huh?" Sans smirked, eyes shut.

"Ooh yeah!" Mettaton exclaimed, enthusiastically.

"Well, whatever happens next is of your own doing." Sans declared, emotionlessly, his eyes reopening to reveal voids of blackness where pupils should be.

Mettaton swerved out of the way of one of Sans' blasts with his new wings. He then returned fire with a neon projectile shot from his arm-cannon. The attack missed Sans and exploded against the wall. The explosion demolished the wall, creating a passage into Hotland. Mettaton flew outside, turning back to Sans and yelling out.

"Hey, tell Alphys I said goodbye, bonehead!" Mettaton howled with laughter, soaring off to hunt the child.

"Not so fast." Sans hissed, swinging his arm down. Suddenly, Mettaton's body crashed into the ground.

"Ugh, just give up already! Is the human's life really that important to you?!" Mettaton snapped.

"I made a promise. I've never made a promise before and I'll never make a promise again. I made one promise to the woman I love. Trust me; I have every intention of keeping it." Sans growled. Mettaton dragged himself to his feet.

"Look, Sans, I'll make a deal with you: if I don't kill the child, can you please not kill me?" Mettaton pleaded.

"Too late for that. I gave you a lot of warnings and now I'm not feeling so merciful."

"Oh, that's a shame… for you…" Mettaton grinned, discharging several rounds of fist-sized neon missiles at Sans. Yet again, Sans sidestepped rapidly, evading again and again. He then propelled roughly a dozen bones at Mettaton who, with a volley of purple rockets, obliterated every single one.

"Impressive. But you're gonna have to do a lot better than that!" Sans laughed, summoning another eight dragon heads. One by one, they blasted straight and Mettaton who swerved and pivoted away from every blast. Mettaton then took to the skies again and, despite Sans' gravity manipulation, managed to stay in the air. He then blasted repeatedly at Sans who, as per usual, didn't struggle to evade every shot.  
"Well, Sans, this has been fun but I guess it's time to end this! After all, the human's nearly here!" Mettaton joyfully announced.

"Don't you dare…" Sans growled.

Sans catapulted bone after bone, Blaster after Blaster, all the while swiping and bending gravity to his will. Constantly teleporting, using all the strength he could muster, Sans desperately and savagely used every trick he had to put down Mettaton for good but to no avail. Worn out and tired, Sans finally flopped to his knees.

"You, uh, really like swinging that thing around, don't ya?" Sans gulped, pointing to Mettaton's gun. "Listen, I know you didn't answer me before but… somewhere within you, there's a good person: I just know it. So, how about it, huh? You and me forget this feud? Maybe go grab some Grillby's? Together? Just you 'n' me, huh?"

Sans outstretched his hand and Mettaton gladly shook it.

"Thank you…" Sans whispered, before several bones erupted from below and pierced Mettaton's body before he even had time to cry out. Every single one of Mettaton's circuits was ripped and broken.

"Get dunked on." Sans chuckled, before the bones went back into the ground, with Mettaton's steel frame still attached to them.

"I g-g-guess you d-don't want to joi-n my f-f-f-fan cl-u-ub?" The deformed pile of scraps spoke before collapsing, gone for good.

"S-Sans? What are you doing?" A shrill cry from behind him rung out.

"Alphys?" Sans questioned.

"What did you do to Mettaton?!" The yellow dinosaur-like monster squealed.

"I, uh, stopped him from hurting the child."

"He wasn't going to…

I swear he was just… please, just… S-S-Sans…" Alphys stammered, tears welling up in her eyes.

"Alphys?" Sans whimpered, putting his arm around her shoulder.

"H-h-he just wanted to chase his dream, Sans," Alphys sobbed, tears streaming down her face, "and now… now he's g-gone…"

She breathed heavily, trying to hold the tears back.

"Hey, Alphys, if you want… I can, uh, help rebuild him and your lab."

"W-what?" Alphys stuttered, bewildered.

"Yeah, sure! I can help you! Er, well, I mean, you're gonna have to do 99% of the work 'cause I have no idea how any of this works. What d'ya say?" Sans smiled.

"Er, sure." Alphys unconfidently grinned, before giggling.

"One small problem though," Sans gritted his teeth, "the human is almost here. We gotta have Mettaton fixed before the kid finds us."

"No problem!" Alphys smiled, before dialling a number in her phone. She put the phone to her ear and said, "Hey, Undyne, could you try and hold of the child for a few hours? Sans and I have got to rebuild Mettaton before the human gets here! T-thanks! Oh, and, Undyne? I was thinking that, maybe, once this was over that we could maybe…"

The hung-up tone from Undyne's end cut off Alphys in the middle of talking.

"Oh." Alphys mumbled. "Anyway, let's get to work!"

After hours of rigorous mechanical work and several dozen robot-related puns, Alphys and Sans were finally done. Mettaton was rebuilt and working again.

"Hey, Sans, thanks for the help!" Alphys grinned.  
"Heh, it's no issue. Anyway, I think the human's just coming into Hotland so you'd better go introduce yourself. Don't worry, I'll slip out the back – the kid won't even see me."

"Oh, okay! Uh, Sans," she asked, readjusting her lab coat, "how do I look?"

"You look, uh, great… really great." He nodded endearingly.

"Aw, thanks, Sans." She grinned, embracing him. He smiled back. Alphys glanced out the window of her lab. "Anyway, I better be off. See ya!" she added, before winking. Then, she descended down the escalator. Sans watched her go, and then hesitated. A couple seconds passed and then he turned and faced the dormant Mettaton lying on Alphys' workbench, eyes shut.

"Alright, bud. Here's how it's gonna work: I'll leave you alone, you go off and do… whatever it is you do… and you stay the hell away from me, my house, my brother and the kid." He spat, turning to leave. Just as he was about to exit the lab, he looked over his shoulder. His eyes reopened, but without pupils.

"Oh, and, uh… tell 'Blooky' I said hi." Sans smirked, and left. Moments passed and Mettaton's screen started glowing again.


End file.
